1. Field of the Invention
The present invention relates to germinated brown rice which can be easily boiled by a household rice cooker and is high in shelf-life stability. The present invention also relates to a process for treating brown rice, by which occurrence of cracked rice kernel or broken rice after drying is reduced.
2. Description of the Background Art
Germinated brown rice is evaluated as functional food because it is good in digestion and uptake and contains nutrient components such as xcex3-aminobutyric acid and ferulic acid in plenty compared with ordinary brown rice. However, cooked germinated brown rice is rough in mouth feel and unpleasant in flavor though the germinated brown rice may be cooked by an ordinary household rice cooker. Germinated brown rice subjected to, for example, steaming for at least 20 minutes, cooling, packaging as it is and heat sterilization, in order to facilitate boiling is broken or cracked in rice kernel because it contains water in plenty and moreover has been subjected to the heat treatment twice. Therefore, such germinated brown rice involves such problems that its appearance after boiling is impaired, it gives stink of bran and sticky feel upon eating and the cooked brown rice becomes quickly hard in mouth feel when it cools. So the use of the germinated brown rice is not always popular. In order to improve its mouth feel, it is possible to apply a process of cooking brown rice by an existing pressure rice cooker, which is performed as a method of cooking the brown rice, to the germinated brown rice. However, such a process involves a demerit of destroying rich nutrients of the germinated brown rice, such as vitamin B.
The germinated brown rice itself absorbs water in plenty in a germination process thereof, and so its shelf-life stability becomes poor and a problem arises from the viewpoint of distribution. Therefore, it has been necessary to cope with such a problem by, for example, vacuum packaging a small amount of heat-treated germinated brown rice, such as an amount of one meal, and further heat sterilizing it. When the germinated brown rice is vacuum packaged, however, a problem of handling arises when it is used in processed food of the germinated brown rice or for business purpose. Therefore, such treated germinated brown rice involves a problem that it is lacking in general-purpose properties from the viewpoints of processability and distribution property.
It is considered to dry germinated brown rice as a means for enhancing the shelf-life stability and distribution property of the germinated brown rice. However, the germinated brown rice, in which water has been contained in plenty in the germination process, involves a problem that cracking or breaking of rice kernel is often caused and its yield after the drying is lowered. On the other hand, it is also conducted to slow the drying speed to prevent the occurrence of cracked rice kernel and broken rice. However, it takes a considerably long time to dry the germinated brown rice to an ideal water content for improving shelf-life stability. There has thus been a demand for an effective means for industrially drying germinated brown rice.
It is a first object of the present invention to provide germinated brown rice which can be easily and deliciously cooked even by a household rice cooker without impairing its original nutritive value, and at the same time, is not accompanied by marked deterioration of mouth feel even when cooked germinated brown rice cools and moreover has excellent shelf-life stability.
A second object of the present invention is to provide germinated brown rice which can be cooked easily and has excellent shelf-life stability and is reduced in occurrence of cracked rice kernel or broken rice.
The present inventors have carried out an extensive investigation. As a result, it has been found that the first object can be achieved by controlling the water content, degree of gelatinization and preferably water absorption upon immersion in water of germinated brown rice. It has also been found that the second object can be achieved by controlling the water content and degree of gelatinization of germinated brown rice by subjecting the germinated brown rice to a steaming treatment or heat-moisture treatment and drying the treated germinated brown rice.
According to the present invention, there is thus provided germinated brown rice the water content of which is 10 to 18% by mass and the degree of gelatinization of which is 5 to 50%.
The germinated brown rice according to the present invention may preferably have a water absorption rate of 110 to 140% upon immersion in water.
According to the present invention, there is also provided germinated brown rice obtained by subjecting germinated brown rice to a heat-moisture treatment and drying the treated germinated brown rice to a water content of 10 to 18% by mass and a degree of gelatinization of 5 to 50%.
According to the present invention, there is further provided a process for treating germinated brown rice, which comprises removing water attached to the surface of the germinated brown rice to an extent that the germinated brown rice becomes an almost single kernel state, subjecting the germinated brown rice of the almost single kernel state to a heat-moisture treatment and then drying the treated germinated brown rice to a water content of 10 to 18% by mass and a degree of gelatinization of 5 to 50%.
According to the present invention, there can be provided germinated brown rice which can be cooked easily and has excellent mouth feel and shelf-life stability. According to the present invention, there can also be provided a treating method of germinated brown rice which can be cooked easily and has excellent shelf-life stability and is reduced in occurrence of cracked rice kernel or broken rice.
The water content in the germinated brown rice as referred to in the present invention may be generally 10 to 18% by mass, preferably 12 to 18% by mass, more preferably 13 to 16% by mass. If the water content is lower than 10% by mass, each kernel of such germinated brown rice tends to cause cracking or breaking, and so such germinated brown rice involves a problem that the taste of cooked germinated brown rice is impaired. If the water content exceeds 18% by mass on the other hand, mold, bacteria and the like are easy to gather, and so a problem arises from the viewpoint of shelf-life stability.
The degree of gelatinization as referred to in the present invention means a value determined in accordance with the xcex2-amylase.pllulanase method (BAP method). The BAP method is an excellent method for distinguishing gelatinized starch from raw starch or retrograded starch. The degree of gelatinization of the germinated brown rice according to the present invention may be 5 to 50%, preferably 5 to 30%, more preferably 10 to 20%. If the degree of gelatinization of the germinated brown rice is lower than 5%, such germinated brown rice involves problems that it is rough in mouth feel when boiled together with polished rice and that an incidence of cracked rice kernel or broken rice becomes high upon its drying. If the degree of gelatinization exceeds 50% on the other hand, blocking among rice kernels occurs, and so handling in the drying process becomes hard, and drying efficiency also becomes poor. In addition, when the germinated brown rice is blended with polished rice to boil the blend, only the germinated brown rice becomes too soft, and so balance of mouth feel after the cooking becomes poor.
The degree of gelatinization can be controlled to the desired value by, for example, suitably adjusting conditions of the heat-moisture treatment and drying in the production of the germinated brown rice. For example, when drying speed is made mild like solar drying to subject the germinated brown rice to no heat treatment, the degree of gelatinization amounts to about 5 to 15%. When the germinated brown rice is steamed at 98xc2x0 C. for about 5 to 20 minutes, or heated and dried at 60xc2x0 C. for about 40 minutes or at 80xc2x0 C. for about 25 minutes, the degree of gelatinization amounts to about 10 to 50%.
The water absorption upon immersion in water as referred to in the present invention is found by using water of 25xc2x0 C., immersing a germinated brown rice sample at room temperature for 30 minutes in water and dividing the weight of the germinated brown rice sample after immersion by the weight of the germinated brown rice sample before the immersion and is expressed by %. In the present invention, the water absorption rate upon immersion is preferably 110 to 140%, more preferably 112 to 138%. If the water absorption rate is lower than 110%, the boiled germinated brown rice is half-done, and rice kernels after cooled become hard and have a dry mouth feel. If the water absorption rate exceeds 140% on the other hand, such germinated brown rice looses its shape when it is cooked, and the germinated brown rice tends to have a sticky feel. Therefore, not only a mouth feel, but also its appearance is spoiled. The water absorption upon immersion is also related to the water content in the germinated brown rice. Germinated brown rice having low water content is high in water absorption, and germinated brown rice having high water content is low in water absorption. However, the water absorption upon immersion is greatly affected by not only water content, but also peeling off and damage of the surface of germinated brown rice. Accordingly, the water absorption rate can be controlled by controlling the water content and conducting peeling. The more the surface of germinated brown rice is peeled, the more its water absorption rate is made high.
The water content, degree of gelatinization and water absorption upon immersion can be controlled to respective desired values by determining conditions of peeling, heat-moisture treatment and drying by conducting experiments properly.
The germinated brown rice according to the present invention can be prepared in accordance with, for example, the following process.
Brown rice is immersed in a germination tank (tank for germination) as it is or after a part of the brown rice is peeled off by a rice whitening machine, rice washer or the like to cause peeling off and damage of its surface, and the thus-obtained brown rice is washed 2 to 4 times with water and then dewatered. The peeling may be conducted after the immersion. The brown rice may be peeled to preferably 95 to 99.8% by mass, more preferably 97 to 99% by mass. By such a treatment, foreign matter and microorganisms attached to the surface of the raw brown rice can be removed, and the amount of water required of rice washing can also be reduced. As described above, the degree of peeling affects the water absorption upon immersion and percentage germination. Therefore, the degree of the peeling can preferably be determined taking this point into consideration. The water used in the rice washing may be any of tap water, distilled water, well water, acid water, electrolytic brine, water in which ozone has been dissolved, etc. so far as it is water usable for food.
With respect to conditions of immersion in the germination tank, there is a method that the brown rice is immersed in warm water of generally 20 to 50xc2x0 C. until the brown rice is germinated, or immersed for, for example, about 3 to 5 hours, dewatering is conducted thereafter, and water spraying is intermittently conducted to germinate the brown rice for the predetermined period of time under high-humidity conditions. As examples of the warm water used, may be mentioned the water described in the rice washing process, and any water may be used so far as it is water usable for food.
The germination may be conducted to a state that a swelling, protuberance or plumule of about 0.5 to 2.0 mm from an embryo can be recognized. After the germination, the germinated brown rice is subjected to a heat treatment in order to stop germination. In order to stop germination, the germinated brown rice may be steamed, or treated at a proper temperature or dried by a suitable method such as the use of hot air or microwaves or cooling.
The germinated brown rice is discharged from the germination tank to transfer it to the next drying process. Before drying, it is preferred that water attached to the germinated brown rice be removed to an extent that the germinated brown rice becomes an almost single kernel state, and the germinated brown rice be subjected to a heat-moisture treatment and then dried. The single kernel state means a state that most of kernels of the germinated brown rice are not bonded to one another with water attached to the surfaces thereof. By this state, handling upon the heat-moisture treatment and drying process is conducted with ease, and so attachment of kernels to one another or a wall surface of an apparatus, unevenness of degree of gelatinization and drying irregularity can be prevented, and drying efficiency can also be improved. The removal of water attached to the surfaces can be conducted by, for example, putting the germinated brown rice discharged on a draining conveyer. At this time, the water attached to the surfaces can be efficiently removed by vibrating the conveyer or conducting ventilation. It is more preferred that agitation be conducted by a rotating blade having a agitating function, screw or the like as needed.
Specifically, the heat-moisture treatment is a process in which a subject is heated by using, as a heating medium, saturated steam or hot water in a high-humidity atmosphere, for example, an atmosphere of at least 60% humidity. In this case, either a heating method in which the subject to be heated is brought into direct contact with the heating medium or a heating method in which the subject is brought into indirect contact with the heating medium like an indirect heating system, for example, in an atmosphere of at least 60% humidity may be performed. With respect to specific conditions, the treatment may be conducted, for example, at a steam temperature of 98 to 180xc2x0 C. for 3 seconds to 30 minutes. If the steam temperature is lower than 98xc2x0 C., the time required for the desired gelatinization is elongated. Therefore, such a low steam temperature is not very preferable when industrial mass production is performed. If the steam temperature exceeds 180xc2x0 C. on the other hand, a problem that the gelatinization is allowed to too progress is caused, and so the immersion time is limited, and the mouth feed of boiled germinated brown rice is deteriorated when the immersion is conducted for a long period of time. If the treatment time is shorter than 3 seconds, irregularities may occur on the degree of gelatinization of rice kernels, and the control in the practical process is also difficult. If the treatment time exceeds 30 minutes on the other hand, the gelatinization of the germinated brown rice is allowed to too progress, and the swelling of rice kernels occurs. Therefore, kernels of the resulting germinated brown rice are easy to be collapsed when the germinated brown rice is blended with polished rice and immersed for a long period of time.
A steaming treatment of rice, which is used in boiled rice production, fermentation industry and the like, may be mentioned as an example of another method than the above-described method. Specifically, for example, brown rice subjected to the germinating treatment is treated with steam for 3 seconds to 30 minutes, preferably 10 seconds to 30 minutes under conditions of 0.1 to 7.0 kg/cm2, preferably 0.1 to 2.0 kg/cm2. If the steam pressure is lower than 0.1 kg/cm2, the preventive effect on the occurrence of cracked rice kernel or broken rice is lessened. The same shall apply to the treatment time shorter than 3 seconds. If the treatment time is too long on the other hand, the gelatinization is allowed to too progress, and so the resulting germinated brown rice tends to deteriorate the mouth feel when boiled together with polished rice, easily cause blocking between kernels and deteriorate handling in the drying process. On the other hand, even if the steam pressure exceeds 7.0 kg/cm2, the preventive effect on the occurrence of cracked rice kernel or broken rice is achieved. However, too high pressure involves a problem of safety.
The drying may be conducted by any of convective (hot air) drying method, radiation drying method, indirect drying method, evenly heating method by electromagnetic waves or the like, vacuum drying method, lyophilization method, etc.
When tempering is conducted before the desired water content is reached in the drying process, beautiful finish can be achieved, and the occurrence of broken rice can be reduced to a greater extent.
When the raw brown rice is peeled in advance, the drying time can be shortened, and it is possible to soften hard pericarp and lessen emission of offensive smell. When a part of surface of the germinated brown rice is whitened to peel off or damage it, it is also possible to more soften hard epidermis and lessen emission of offensive smell.
The germinated brown rice according to the present invention may be used for food by boiling it either singly or in combination with brown rice or polished rice, or as a raw material of rice confectionery such as rice crackers, and processed foods such as bread and behon. As needed, intensification of nutrition may be conducted with functional components such as vitamins, minerals, xcex3-orizanol, tocotrienol and ferulic acid by a proper treatment such as water absorption by immersion or coating.
The present invention will hereinafter be described in detail by the following Examples.